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bfagioli
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power usage -- run on 2-AA batteries?

Sun Aug 04, 2013 5:10 pm

I have a model B and the camera board. Having lots of fun so far:) I've recently done this "dash cam" project where I use raspistill in timelapse mode. The pi is powered by the car via a usb converter in the lighter. This has worked fine but now I want to do a "bicycle cam" so I'll need portable power. The byicycle trip I have in mind will be about 80 minutes and I want to be able to run raspistill in timeplase for the entire time. How much power does the camera board consume when in time lapse mode? BTW, I have disable its LED to conserve power.

Here are some details:

- The battery to USB device I plan to use:
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0153735517

- My batteries will be NiMH and are 1.38V when fully changed

- My Pi is model B. No peripherals except an 8GB flash drive (but I could do without this). Stock Raspian OS running, starts a cron job that starts rasbistill timelapes and also starts X window system (could do without that).

So, do you think I'll be able to power that configuration for 80 minutes on 2-AA or would I need a 4- or 6-AA battery pack?

Thanks
-Bob

tvoverbeek
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Re: power usage -- run on 2-AA batteries?

Sun Aug 04, 2013 5:31 pm

Short answer: will not work (probably)
Longer answer: According to the ebay listing the max current is 500 mA at 5V.
I am assuming the device uses a switching regulator to boost the voltage from 3 to 5 V.
Pi model B uses about 400 mA and the camera when active may use an other 350 mA.
The total is above what your device can supply.
For some background see Dave Akerman posting about running the Pi from batteries (which
he has to do for his balloon flights): http://www.daveakerman.com/?page_id=1294.
The posting contains some formulas to estimate how long you can run on batteries.
Also look at http://www.raspberrypi.org/phpBB3/viewt ... 6&p=391268
for some real life current measurements.
The ethernet port on the model B uses quite a bit, even if not used. See also Dave's posting about how to turn of HDMI when not needed.

Good luck with running Pi+Camera on batteries.

Ton van Overbeek

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jojopi
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Re: power usage -- run on 2-AA batteries?

Sun Aug 04, 2013 5:55 pm

If you can film without Ethernet and USB, which seems possible in this application, then see this thread about stopping the LAN9512 chip: http://www.raspberrypi.org/phpBB3/viewtopic.php?t=16093

Better still is to start with a Model A, though.

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bfagioli
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Re: power usage -- run on 2-AA batteries?

Sun Aug 04, 2013 6:04 pm

tvoverbeek wrote:...and the camera when active may use an other 350 mA.
Wow that's way more than I thought. Looks like I'll need more power

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bfagioli
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Re: power usage -- run on 2-AA batteries?

Sun Aug 04, 2013 8:51 pm

I don't have to worry about extra weight like that hot air balloon project (which is very cool btw) so I can add more batteries but I guess I need a different USB converter device. If I had one that was capable of outputting 5V and upto 1A that should be enough right?

So what about this device:
http://www.ebay.com/itm/DC-DC-Converter ... 53f8b64805

and if I combine that with a 4 or 6 AA NiMH batteries.

Do you think that would supply enough power for my configuration and handle a duration of 80 minutes?

Thanks

poing
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Joined: Thu Mar 08, 2012 3:32 pm

Re: power usage -- run on 2-AA batteries?

Mon Aug 05, 2013 12:13 pm

If you put 4 AA batteries in series without any circuitry the voltage will be 4x1.38=5.52V when full and 4x1.2=4.8V when depleted. But the 5.52V will be lower when the Pi with camera is drawing power. Should work fine I guess.

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RaTTuS
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Re: power usage -- run on 2-AA batteries?

Mon Aug 05, 2013 12:50 pm

How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

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bfagioli
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Re: power usage -- run on 2-AA batteries?

Mon Aug 05, 2013 1:13 pm

RaTTuS wrote:http://www.amazon.co.uk/Portable-Powerb ... 00CI3DG8K/
will work for 16+ hours
That looks powerful. I prefer a solution that lets me reuse my existing AA NiMH batteries because I have many of them.

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bfagioli
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Re: power usage -- run on 2-AA batteries?

Mon Aug 05, 2013 5:02 pm

poing wrote:If you put 4 AA batteries in series without any circuitry the voltage will be 4x1.38=5.52V when full and 4x1.2=4.8V when depleted. But the 5.52V will be lower when the Pi with camera is drawing power. Should work fine I guess.
The 2nd device I referenced (my most recent post) says that it can take input voltage from between 2.4 - 6V and deliver 5V output. So it seems like its both a "step up" and a "step down" converter depending on the battery level. In output amps it supports is up to 1000mA. I already have a battery case for 4 batteries with lead wires, 4 NiMH batteries and a micro USB cable. So, I just need to get this device, do some soldering and it should be able to power the Pi, Camera, and thumb drive right? Anyone see a problem with this plan?

THanks

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bfagioli
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Re: power usage -- run on 2-AA batteries?

Wed Aug 28, 2013 4:15 am

Here is what I ended up with.

PARTS LIST:
  • 1. I several old Kodak NiMH 2100 mAh batteries around the house so they are essentially free (to me :) ).

    2. USB DC to DC 5V Voltage Step Up Boost Module for $2.20 US from dx.com. The specs say the ouput max is 500 mA but people were revewing the product saying that it can output a max of 1A so I took a chance and the 1A seems to be true. http://dx.com/p/usb-dc-1-5v-to-dc-5v-vo ... een-143571

    3. 4 x AA Battery Holder Case Box with Leads for $1.90 US from dx.com. It has a nice little on/off switch. http://dx.com/p/6v-4-x-aa-battery-holde ... ads-103856
RESULTS:
In my first test I had my USB nano WiFi attached and operating, 2nd USB port was connected to powered USB hub for keyboard and mouse and the hdmi was connected to a monitor. The camera board was operating and I was taking a 5MP still once per minute. In this configuration the Pi ran off my 4 AA batteries for 70 minutes. I was encouraged. For my bike cam project I want to take a still every 10 seconds for 60 minutes.

My 2nd test was with no peripherals attached at all. The Pi boots and runs a simple cron job that writes a time stamp to a file. The camera board is still connected but I did not use it. In this bare-bones test my 4 AA battery pack provided power for 4 hours.

So, bottom line is that my very inexpensive ($4.10 US) battery solution may be able to provide the power I need for my 60 minute bike cam project -- but 2 AA is just not enough power.
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RaTTuS
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Re: power usage -- run on 2-AA batteries?

Wed Aug 28, 2013 7:53 am

also I have a digital volt meter on my camera RPi fixed between TP1 TP2
which currently [HA!] measures 4.88V with no camera and 4.79 when the camera is active
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

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bfagioli
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Re: power usage -- run on 2-AA batteries?

Wed Aug 28, 2013 1:24 pm

RaTTuS wrote:also I have a digital volt meter on my camera RPi fixed between TP1 TP2
which currently [HA!] measures 4.88V with no camera and 4.79 when the camera is active
I have been monitoring the voltage reading between TP1 & TP2 also. I thought that was the voltage that the Pi was receiving from the power source. Do you have an explanation why the volts drop when the camera is active -- I'm just curious.

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leol
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Re: power usage -- run on 2-AA batteries?

Wed Aug 28, 2013 1:31 pm

bfagioli wrote:
RaTTuS wrote:also I have a digital volt meter on my camera RPi fixed between TP1 TP2
which currently [HA!] measures 4.88V with no camera and 4.79 when the camera is active
I have been monitoring the voltage reading between TP1 & TP2 also. I thought that was the voltage that the Pi was receiving from the power source. Do you have an explanation why the volts drop when the camera is active -- I'm just curious.
It is the voltage that the Pi and the Camera is receiving and indicates that the power supply is unable to maintain the voltage when the camera draws its required current.

You need a better power supply.

Leo

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RaTTuS
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Re: power usage -- run on 2-AA batteries?

Wed Aug 28, 2013 1:35 pm

no - not exactly sure- [it's on of the reasons why I'd done this] it could be that my supply is very marginal and when the camera is active it's just pulling a bit too much....
I've got to have a look at this a bit more
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

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bfagioli
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Re: power usage -- run on 2-AA batteries?

Wed Aug 28, 2013 2:11 pm

At what voltage will the Raspberry Pi just stop working? When the pi is halted but power is still on the voltage reads 5.05 but when the pi starts up that drops to 4.80. If I use the camera it drops further to 4.72. This is with my ac power. With the battery pack voltage starts lower at say 4.70 and continues to drop over time. I am running raspstill in time lapes mode taking a still every 10 sec. Running the test now and tp1&2 read 4.45 but is still operating -- as far as I can tell.

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bfagioli
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Re: power usage -- run on 2-AA batteries?

Sat Aug 31, 2013 8:32 pm

I was finally able to answer my original question -- can you run a model B on 2 AA batteries and operate the camera board? Short answer: Yes.

Using this very inexpensive (1.85$ USD) USB charger and my own 2 AA batteries I was able to power my model B for 67 minutes and using the camera board to snap a still every 10 seconds. This device says that its max output is 500 mAh but that has to be wrong.

This is a really inexpensive possibility especially if you only need power for short periods of time.
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